1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) technology, and mare particularly, to a direct-light type backlight module and an LCD.
2. Description of the Prior Art
Cold cathode fluorescent lamps (CCFLs) used to be backlight sources of an LCD. However, LEDs have been substituted for most CCFLs and become the mainstream light sources on the market. This is because LEDs have advantages of becoming flatter, consuming lower power, and containing no mercury. Moreover, the LEDs have been used in direct-light type backlight modules gradually.
Low-cost direct-light type backlight modules use LEDs mounted by surface mount technology (SMT) and use a secondary optical lens as well. In such LCD technology, a type that maximum luminous intensity occurs at a wide viewing angle replaces the lambertian scattering light pattern (LEDs emit light). Referring to FIG. 1. FIG. 1 shows a diagram of refraction of light emitted by an LED in the secondary optical lens 102 in a conventional direct-light type backlight. A light source 101 is an LED and is disposed under the secondary optical lens 102. The center of the secondary optical lens 102 is concave. The concave center could deflect light emitted by the light source 101 at a frontal viewing angle to emitting light at a wide angle. Therefore, the formed light pattern is transformed from the lambertian scattering light pattern into the wide angle scattering light pattern. As shown in FIG. 2 and FIG. 3, FIG. 2 is a coordinate diagram showing a relation between brightness and viewing angles in the lambertian scattering light pattern formed when an LED light source without the secondary optical lens emits light. In FIG. 2, x-coordinate indicates viewing angles, and y-coordinate indicates brightness of light. FIG. 3 is a coordinate diagram showing the relation between relative brightness and viewing angles of the wide viewing angle light pattern shown in FIG. 1. In FIG. 3, x-coordinate indicates relative brightness of light, and y-coordinate indicates viewing angles. As can be seen, the wide viewing angle light pattern combining with the secondary optical lens could reduce the number of LEDs, which helps reduce production costs.
However, a serious technical problem would occur when the wide viewing angle light pattern is realized in the direct-light type backlight module. Whenever light emitted at a wide viewing angle usually shines on support pins which support a diffuser plate, a shadow is produced. Referring to FIG. 4, FIG. 4 shows a location relationship diagram of a support pin 402 and a light source in a conventional direct-light type backlight module. As shown in FIG. 4, due to a shielding effect of the support pin 402, a luminous domain 403 is formed on the upper part of the support pin 402, and a shadow is formed at one side of the support pin 402 against light which is emitted by an LED 401 (the light source) and shines on the support pin 402. In other words, an emitting surface of the direct-light type backlight module would produce a stripe of shadow on one side of the support pin 402 against the LED 401, which is called “support pin shadow mura.” Referring to FIG. 5, FIG. 5 shows a schematic diagram of support pin shadow mura generated when light is blocked by the support pin 402 in FIG. 4. As shown in FIG. 5, a domain 403′ represents the shadow after light emitted by the LED 401 is blocked by the upper part of the support pin 402. As can be seen, an emitting effect of the direct-light type backlight module is affected.
Therefore, there is a need for a direct-light type backlight module for preventing support pin shadow mura occurring in the conventional technology.